This isn’t my normal kind of post, but I’ve seen a lot of people terrified about this over the last couple of days — people seriously worried that they are going to catch, and die from, ebola, because of the news coverage of it. People are worried about “pandemics”, “apocalyptic plagues” and the like.
So in order to do my bit for calming people down, I thought I’d present the facts, as simply as possible. Now, I’m not a doctor, but if you’re seriously worried about getting ebola, neither are you (unless you’re a doctor in Guinea, Sierra Leone, or Liberia, in which case you probably need a better resource than my blog). This is not medical advice, just general reassurance.
The simple takeaway is this — you are not going to get ebola. If you want, you can stop reading now — that’s all you need to know. But you can also carry on reading and find out *why* you’re not going to get ebola.
Here are the facts. The only people who’ve caught ebola at present are in Guinea, Sierra Leone, and Liberia. If you’re there, you may be in some danger. But not much. 728 people have died of ebola in those countries, combined, in the last five months. That’s a lot of people, dying in a very unpleasant way, but it’s 0.00364% of those countries’ populations. In statistical terms the total number of people in the world with ebola is a rounding error. On average, 6000 people a year die of lightning strike, so nearly four times as many people will have died from lightning in the same period that those people died of ebola. We simply don’t have words in the English language for how unlikely dying of ebola actually is.
That’s why it’s on the news, of course — if something hardly happens at all most of the time, then happens a little bit, that seems like a bigger news story than something that happens a lot carrying on happening.
But, of course, lightning isn’t contagious — you can’t catch “getting struck by lightning” from someone else. So are people still right to be worried?
No, because to all intents and purposes ebola isn’t contagious either.
This may sound surprising, but the fact is that ebola can only be caught by contact with the bodily fluids (things like urine, semen, blood, and vomit) of someone with ebola, and not just normal contact — you either have to get them in your blood (for example getting some on an open wound), or they have to get on your mucous membranes (areas like the genitals, anus, or eyelids).
In other words, the transmission happens in much the same way as HIV gets transmitted, and can be prevented the same ways — don’t have unprotected sex, don’t share needles, don’t clean up other people’s bodily fluids without wearing gloves, and if you *do* clean up bodily fluids, use disinfectant and make sure you clean them up properly. We know how to control this kind of infection. There’s a reason it mostly spreads in very poor countries — because those countries can often not afford high levels of health care, and the responsibility (especially in the early stages of the illness, when it seems like flu) falls on family members who haven’t had proper training in dealing with contaminated materials, or on hospitals which have no choice but to reuse needles because they can’t afford disposable ones.
But if it’s transmitted the same way as HIV, won’t it spread as widely as HIV? After all, there are tens of millions of people worldwide with that…
No, it won’t. And the reason is simple. On average, an untreated person with HIV goes ten years between getting infected and getting AIDS symptoms (and of course someone who’s being treated can go indefinitely without AIDS symptoms), but they’ve got the virus all that time. That’s ten years in which they can infect other people.
Ebola, on the other hand, makes sufferers sick within two weeks. Most of them die very quickly (and the rest get better within about seven weeks). This is, of course, a very bad thing for the individual sufferer, but it’s much, much, better for the population at large, because it means there’s not much time for them to infect anyone else, so ebola outbreaks burn out quickly.
Ebola is a horrible, horrible disease, and I don’t want for a second to suggest that concern for the victims is misplaced. Everything reasonable should be done to make sure the disease is eradicated. But don’t be concerned for *yourselves*. You’re far, far more likely to die from the stress you cause yourself worrying about ebola than you are from ebola itself…

I’m pretty sure that as Ebola reaches us, we’ll keep on top of it, but it’s clearly got out of control in Africa, spreading exponentially. Talk of 10,000 cases per week may not be an exaggeration. We need to start doing something very soon to help the people there, and disease is much easier to stop while it’s in its early phase.

Also, I’m not sure how much epidemiology you know, but there’s a value used to describe how easily a disease can spread, called the “basic reproduction ratio”, denoted R0. This value is the expected number of secondary cases from a primary case while the spread isn’t limited by availability of susceptibles. For HIV, R0 is about 4, which means each infected person tends to pass it on to about four more. You’re right that Ebola is not particularly infectious, as its R0 is only 2, but for a disease to spread the only requirement is that R0>1 (for comparison, measles is considered highly infectious, and has an R0 of 18).

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